2008-07-10_PERMIT FILE - M2008006 ‎(3)‎

• Permit No: M2008006
• IBM Index Class Name: Permit File
• Doc Date: 7/10/2008
• Doc Name: Floodplain Development
• From: Connell Resources
• To: DRMS
• Media Type: D
• Archive: No

the most acceptable way to model and understand the effects of the reclaimed site conditions
would be to create an existing model with the updated topography for the site that can be
' compared to the proposed model.
Three cross sections across the site were cut using the updated topography and then converted to
the NGVD 29 datum for use in the existing model. There were no indications that the land use and
' ground cover has changed drastically since the creation of the effective model. Therefore, the
Manning's n values used in the effective model remain valid and were used in the existing model.
Information relating to the floodplain permit for property east of the Serfer Property was
unavailable from Larimer County, Weld County, Town of Windsor and Anderson Consulting. ,.
' Therefore, we left the hydraulic model unchanged to the east of SerFer property.
The effective model was modified to reflect the updated topography for the site. Cross Sections
153515, 154485 and 155595 in the HEC-2 model were updated; these relate to cross section C, D
' and E on the work maps. Updating these cross sections results in the following changes to the
model shown in Table 1 below:
Existing Conditions Water
Elevation Surface Elevation
NA 148960 4780.7 4780.7 0.0
' NA 149580 4781.35 4781.35 0.0
NA 151100 4782.85 4782.83 0.0
NA 152250 4785.47 4785.43 0.0
NA 152300 4785.66 4785.63 0.0
*A 152340 4787.65 4787.6 0.0
* B 152390 4787.66 4787.61 -0.1
' *C 153515 4787.84 4787.86 0.0
*D 154485 4789.13 4788.81 -0.3
*E 155595 4790.26 4789.78 -0.5
' F 156815 4793.27 4792.53 -0.7
G 156865 4794.24 4794.39 0.2
H 156905 4794.57 4794.81 0.2
1 156955 4795.15 4795.24 0.1
J 157720 4796.62 4796.61 0.0
K 159000 4797.36 4797.36 0.0
L 159805 4797.75 4797.75 0.0
' On Site Cross Sections
Table 1: Effective vs. Existing Conditions
No other information in the model was altered other than the topography for those cross sections.
Printouts of the input and the output for the HEC-2 model are in the located in Attachment G of this
document. Graphs comparing the cross sections are included for your reference in Attachment E.
'File proposed mining limits for this property are located entirely within the delineated floodway
I for the Cache la Poudre River. In order to eliminate negative impacts on the floodway during the
proposed mining operations, the applicant proposes not to store any stockpiles or overburden at
Serfer Pit Floodplain Development Permit